Hi Jamie,
Like you I was looking for quite some time for the right car to come along. You want the best you can get for your money! I was looking for a 2011+ facelift portfolio s with 20inch wheels and the B+W stereo. 16k is a lot of £s but seems to be the very minimum for a 100k miler. You need a full sevice history and a proven history at the very least and get an hpi check. If you are not mechanically minded, get an RAC check. Worth the £ for peace of mind. But if it feels right, sounds right and drives right, it probably is. Walk away if it doesn't, there's a lot out there if you are not in a hurry. All used cars will have something that needs doing, that's ok, just get the price right.
I bought a 28k mile 2012 premium luxury s with full jag s/h cream leather, privately and got a brilliant deal, not the holy grail but the very best I could have got for my £s! Even the basic models are better than anything else out there.
Good luck mate,
chris